Short answers, pulled from the story.
Takashi Nishiyama created Ken Masters during the development of the original Street Fighter arcade game released in 1987. The character debuted alongside Ryu as one of only two playable fighters due to budget constraints.
Ken started with bare feet and yellow arm bands before gaining dyed-blonde hair and a red sleeveless keikogi in Street Fighter II. By Street Fighter 6, he dropped his signature red gi entirely for a black v-neck training shirt and topknot hairstyle to reflect narrative instability.
Critics noted that the Super Street Fighter II Turbo version became unbalanced to the point of being the strongest character due to powerful movesets. Dave Cook from Now Gamer called him one of the most hated characters because players found him difficult to defeat even with problems regarding his playstyle.
Street Fighter 6 set years later showed Mel as a teenager facing criminal conspiracy manipulated by JP into funding terrorist activities. Deepfake footage framed Ken for taking part in the conspiracy against his will so he went into hiding to protect his family while hunting JP down.
Promotion included an officially licensed NubyTech/UDON joypad announced on the 27th of September 2004 following Evo Moment 37. A Mad Catz joypad featuring Ken was also released for the PlayStation 3 shortly after this event.
Damian Chapa portrayed Ken in the 1994 live-action Street Fighter movie while Scott McNeil voiced Ken in the animated series. Noah Centineo is set to portray Ken in an upcoming reboot of the franchise alongside other actors like Joey Ansah and Christian Howard.